1. Field of the Invention
The present invention relates to an image processing apparatus, which executes color selection processing.
2. Description of the Related Art
Conventionally, a remote-copy function which connects a scanner, printer, and MFP with each other via a network or the like, and outputs a document image input by the scanner or MFP using another printer or MFP via the network is prevalent. Note that the MFP (Multifunction Peripheral) generally indicates a composite peripheral equipment which has a plurality of functions. In the following description, assume that a scanner, MFP, or the like, which inputs a document image upon execution of remote-copy processing, will be referred to as a sender, and a printer, MFP, or the like, which outputs the document image, will be referred to as a receiver.
In general, upon remote-copying a color document image, the sender side compresses color data so as to reduce a network load. As a compression method of color data, JPEG and JPEG2000 as the international standards of still image encoding are generally known. As image data formats which support one or both of JPEG and JPEG2000, PDF of Adobe Systems, TIFF of Microsoft and Aldus, WMP of Microsoft, and the like are known. That is, the JPEG, PDF, TIFF, and WMP formats can be used as principal image data formats upon remote-copying a color document image. Data compressed by the sender side are decompressed and output on the receiver side. Furthermore, the user can arbitrarily set a compression ratio upon compressing data on the sender side. For example, when the user sets a high compression ratio, since the data size can be reduced, data transfer efficiency can be improved, and the memory use size on the receiver side can be reduced. However, the compression ratio arbitrary set on the sender side may deteriorate image quality.
Conventionally, in a color MFP, an ACS (Automatic Color Selection) function is prevalently used. With such ACS function, the number of color pixels in a document is calculated and is statistically processed to check if an input document image is a color or monochrome image. Based on this checking result, image formation using four colors, i.e., C (cyan), M (magenta), Y (yellow), and K (black), or black alone can be made. It is important for such color selection function to solve problems posed when a monochrome document image is undesirably formed using four colors, i.e., C, M, Y, and K colors (for example, wasting of toners, inks, or the like, a quality drop due to slight color misregistration, unwanted color charging for a monochrome document, and so forth).
Japanese Patent Laid-Open No. 2002-44464 discloses a method and apparatus, which can appropriately execute color selection processing of a document in accordance with a document type. According to this method and apparatus, this reference describes that a low-saturation image can be determined as a color image, a low-saturation color character can be recognized as a monochrome character with high visibility, and recognition errors due to color misregistration or the like can be reduced. Also, Japanese Patent No. 2935505 discloses an image processing apparatus and method, which can prevent determination errors of an achromatic color region of an input image. According to this method and apparatus, the reference describes that determination errors due to different reading conditions can be eliminated by changing a threshold used to determine a chromatic or achromatic color in accordance with the drive condition of a drive scan unit in a reading scan unit of a document reader.
However, these references do not particularly describe problems such as outputting of a monochrome document as a color image, and outputting of a monochrome printed part of a color document as a color part in the arrangement in which the remote-copy processing is executed from the sender to the receiver. In such arrangement, for example, when the sender does not have any ACS function, the problems such as printing of a monochrome document as a color image and so forth may occur. In general, a low-profile, low-end scanner such as a flatbed scanner or the like, which attaches an importance on usability does not normally have any ACS function. Therefore, in the remote-copy function, when a scan image is compressed when it is saved in a hard disk or it is sent, monochrome pixels may be changed to color pixels. For example, a monochrome pixel defined by equivalent values R (red)=G(green)=B (blue)=40 may be changed to R=40, G=45, and B=40, thus causing a color fluctuation. As a result, a monochrome document image is changed to a color image, or a monochrome printed part of a color document is changed to a color image.
On the other hand, even when the sender has the ACS function, a problem that a monochrome document is printed as a color image without reflecting an ACS result upon sending may be posed. In the ACS function, the number of color pixels in a document is counted and is statistically processed. Therefore, the processing result is ready in time for local-copy print processing as a normal copy function, but it may not be ready in time for remote-copy sending processing depending on the processing performance of the ACS function in the sender. In such case, the sender transfers data as a color image. As a result, the receiver outputs a color image.
As described above, the problems such as printing of a monochrome document as a color image and the like are often posed irrespective of the presence/absence of the ACS function on the sender side. The receiver may execute color selection processing of color and monochrome documents using the ACS function. However, since the color selection threshold of the ACS function is fixed, deterioration of image quality and color fluctuations caused by a compression ratio arbitrarily set by the user on the sender side cannot be coped with.